Vapor deposition is a common technique used in forming thin films during the production of an integrated circuit (IC) in semiconductor device manufacturing. Vapor deposition is also useful in forming conformal thin films over and within features on a substrate.
Chemical vapor deposition (CVD) processes generally include the introduction of a continuous stream of film precursor vapor into a reactor containing the substrate on a substrate support, which is generally heated to an elevated temperature. The film precursor vapor comprises the principle atomic or molecular species that will ultimately form the thin film on the substrate. Film formation typically occurs when precursor vapor that is chemisorbed onto the heated surface of the substrate thermally decomposes and reacts. Additional gaseous components may be used to assist in the decomposing or reacting of the chemisorbed precursor vapor.
In plasma enhanced CVD (PECVD), a plasma is generated within the reactor and utilized to alter or enhance the film deposition mechanism. For example, plasma excitation may allow a particular film-forming reaction to proceed at substrate temperatures that are significantly lower than conventional CVD temperatures. While PECVD may be used to deposit a wide variety of films at this lower substrate temperature, the use of the plasma may result in high energy ion bombardment or vacuum ultraviolet (VUV) radiation of the substrate during film growth, either of which may result in dangling bonds, trapped free radicals within the deposited film, or damage to the substrate.
In filament assisted CVD (FACVD), the film precursor is decomposed by a resistively heated filament positioned within the process space. The resultant fragmented molecules adsorb and react on the surface of the substrate. Unlike PECVD, plasma formation is not necessary for the deposition process, making FACVD particularly advantageous in reducing damage to the substrate during the deposition process.
However, there continues to be needed improvements within FACVD. For example, film deposition is not limited to the surface of the substrate, but instead may extend to other internal surfaces of the reactor, including the resistively heated filament. These film deposits may peel off during a subsequent deposition process and contaminate the processed substrate. Therefore, it is highly important to provide clean internal surfaces of the reactor.
Moreover, the emissivity of the resistively heated filament changes with surface composition. In that regard, while the same DC power level may be used for various batches, the temperature of the resistively heated filament may, in reality, vary greatly with the addition of film, thereby affecting the decomposing of the film precursor and resultant rates of film deposition onto the substrate. Therefore, it would be advantageous to develop a method to sustain a clean resistively heated filament in order to standardize the operational conditions before each deposition process is initiated. Further, it would be of great benefit to incorporate the cleaning process into the normal operational process of the FACVD system to increase throughput, such as by in-situ cleaning between substrate or batch processing.